Servomechanism



June 18, 1963 v. s. WAGNER 31194-041 SERVOMECHANISM Filed Oct. 7. 1960 6 Sheets-Sheet 1 I; 34 a 256 2o- 44 28 2 was 36 a l6 ssf 234 252 12 6 236 2 FIG. I.

INVEVTOR. VlNCENT S. WAGNER ATTO R NE V. S. WAGNER SERVOMECHANISM June 18, 1963 6 Sheets-Sheet 3 Filed Oct. 7. 1960 FIG. 3.

INVENTOR. VINCENT S. WAGNER BY 4 A um, ATTORNEYS SERVOMECHANISM Filed Oct. 7. 1960 6 Sheets-Sheet 4 210 Mk 2|o 234 15 H 1 .Tffffi F I G, 4.

mmvroa VINCENT S. WAGNER ATTORNEYS June 18, 1963 v. s. WAGNER 3,094,041

sssvouscumxsu Filed Oct. 7. 1960 e Sheets-Sheet 5 FIG. 5.

INVENTOR. VINCENT S. WAGNER ATTOR V. S. WAGNER SERVOMECHANISM June 18, 1963 6 Sheets-Sheet 6 Filed Oct. 7. 1960 FIG. 6A.

FIG. 60.

FIG.6C.

FIG. 6E.

INVENTOR. VINCENT S. WAGNER BY ATTORNEYS United States Patent 3,094,041 SERVOMECHANISM Vincent S. Wagner, Lower Makefield Township, Bucks County, Pa., assignor to De Laval Steam Turbine Company, Trenton, N.J., a corporation of New Jersey Filed Oct. 7, 1960, Ser. No. 61,128 8 Claims. (Cl. 91-375) This invention relates to a servomec'hanism for operating, for example, the valves of a steam turbine, and more particularly to such a mechanism which automatically closes the valves under certain conditions while nevertheless permitting manual operation thereof when necessary.

While the invention described hereafter is applicable to many situations wherein servomechanisms are employed to operate various devices, it will be described particularly in relation to the Operation of the large steam valves generally employed in marine steam turbine propulsion plants. These valves regulate the admission of steam to the turbine nozzles, :and thereby control the power output of the turbine. Usually, the turbine has its own oil system, and it obviously is imperative that when the oil pressure drops due to a failure of the system the turbine should be shut down, which is effected by closing of the steam valves. Also, upon an abnormal increase in the turbine speed, the steam valves are closed to the extent necessary to bring the turbine back to its proper speed or to shut the turbine down if it were to be in a runaway" condition. Such controlling operations preferably are effected automatically. Since the valves are large, direct manual operation thereof is difficult and some form of power operation is desirable. Such power operation may be hydraulical, as specifically disclosed hereafter, using oil from the ships oil system, but in the event of a failure in such system and consequent deactivation of the hydraulic power operator, it should be possible nevertheless to manually operate the valves if necessary.

Accordingly, it is an object of the invention to provide a servomechanism with a power operator for the manual operation of steam valves or the like.

It is a further object to provide such mechanism which is responsive to certain conditions such as a failure in an oil system and/ or an unsafe speed to close or adjust the valves automatically.

It is a further object to provide such mechanism which permits manual operation of valves or the like despite inoperability of the power operator, for example due to a failure in its operating oil system.

Further objects and advantages will become apparent from the following disclosure read in conjunction with the drawings, in which:

FIGURE 1 is a flow diagram of a typical hydraulic circuit and a schematic illustration of the servomeehanism operably connected to the turbine steam valves;

FIGURE 2 is a vertical axial cross-section of the servomechanism;

FIGURE 3 is a transverse cross-section taken on line 33 of FIGURE 2;

FIGURE 4 is a cross-section taken on line 44 of FIGURE 2;

FIGURE 5 is a plan view of the servomeohanism, with a portion thereof shown as a cross-section taken on line 5--5 of FIGURE 3; and

FIGURES 6A to 6B inclusive schematically illustrate the relative positions of the pilot valve and vane during various stages of operation.

Referring to FIGURE 1, the servomechanism for operating the turbine steam valves is indicated at 2, and hereafter for purposes of description this mechanism will be referred to briefly as the operator. A bank of valves 4 is provided within the steam chest 6 to individually regulate the admission of steam to chests as indicated at 3,094,041 Patented June 18, 1963 8 associated respectively with groups of the turbine nozzles. Each of the valve members 10 has a threaded stem on which are looked a pair of nuts 12 adapted for engagement by a valve lifting bar 14. The bar 14 is adapted to be raised and lowered by a pair of rods 16 and 18 operated, respectively, by cam assemblies 20 and 22. It will be noted that the nuts 12 of the respective valves are positioned at various heights with respect to their valve stems. The purpose of this arrangement is that it is desired not to open all of the valves simultaneously, but to open the valves in sequence, one at a time, and as the bar 14 is lifted it will engage the fixed nuts of certain valves to lift and open them prior to the opening of other valves. The cam assembly 22, which is identical with cam assembly 20, is shown in cross-section to illustrate the operating parts thereof. A shaft 24 (which is common to assemblies 20 and 22) is journalled in the housing 26 of assembly 22 and connected to an output shaft 28 of the operator 2 by a coupling 30. An eccentric cam 32 is keyed to shaft 24, and a cam follower mechanism therefor comprises a plurality of rollers 34 in circumferentially spaced engagement with the cam 32. Rollers 3-4 are rotatably mounted by pins 36 in a cage 38 connected to the rod 18. Thus it will be evident that rotation of cam 32 effects reciprocation of rod 18 to raise and lower bar 14. It will be understood that the above described structure of cam assembly 22 is identical with that of assembly 20, and the two assemblies are jointly acting on the bar 14. A pair of collars 40 and 42 are integral with shaft 24, and between these collars and the respective adjacent housings of assemblies 20 and 22 a pair of torsion coil springs 44 and 46 are concentrically mounted on the shaft. Spring 44 is a right hand helix and spring 46 is left hand helix, and the effect of this arrangement is that rotation of shaft 24 in a clockwise direction, as viewed from the left end in FIGURE 1, is resisted by the coiling of springs 44 and 46.

Passing now to description of the specific operator structure 2, reference will be made to FIGURES 2 to 5. The main body of the operator housing, generally indicated at 48, may consist of a single steel casting. The left end (FIGURE 2) of housing 48 has the form of a drum or cylinder 50 which is closed at one end by a head 52 secured to the housing by a positioning taper pin 54 and bolts 55, and is closed at its other end by a cast-in wall 56. A sleeve 58 passes axially through cylinder 50 and is rotatably mounted at its left end (FIGURE 2) by a bushing 60 and oil seal 61 in head 52, and at its right end by a bushing 62 mounted in an annular flange 64 extending from wall 56. A pair of vanes 66 and 68 extend radially from sleeve 58 and are mounted thereon by bolts 70. The vanes 66 and 68 are identical, the vane 66, for example, being substantially cup-shaped and comprising a back wall 72, an arcuate end 74 closely fitting the cylinder 50, and side Walls 76 and 78 closely fitting, respectively, the head 52 and wall 56. As will be seen hereafter the vanes 66 and 68 are, in eifect, similar to pistons movable within cylinder 50. Vanes 66 and 68 are milled away or cast at 80 and 84 to expose, respectively, ports 82 and 86 in the wall of sleeve 58.

A member 88, hereafter referred to as the pilot valve, is closely fitted and rotatably received within sleeve 58. Pilot valve 88 has a circumferential groove 90 which is axially aligned with ports 92 and 94 in the sleeve 58 and bushing 62, respectively, and with a continuous circular channel 96 in wall 56. Pilot valve 88 has a second circumferential groove 100 axially aligned with ports 102 and 104 in sleeve 58 and bushing 60, respectively, and with a channel 106 in head 52 extending around bushing 60 and communicating with a passage 108.

Pilot valve 88 has flat portions or lands 98 and 99 3 (FIGURE 3) extending axially from groove to th extent indicated at 101. Extending rightwardly in (FIG- URE 2) from groove pilot valve 88 has a pair of channels and 107 which terminate short of the groove 90.

A pair of opposed tapered abutments 110 and 112 extend horizontally from the cylinder 50 (FIGURE 3), from which they are supported by bolts 114. Pins 116 and 118 anchor the abutments to the wall 56 and head 52, respectively. A passage 120 in abutment 112 is aligned with an opening 122 in head 52, and terminates in the upwardly opening passage 124.

Vane 110 has a similar passage 126 which is aligned with an opening 128 in head 52 and terminates in the downwardly opening passage 130 (FIGURE 3). Passages 132 and 134 (FIGURE 5) provide communication between openings 122 and 128, respectively, and channel 106, which in turn communicates with passage 108 as previously mentioned.

The exposed end of sleeve 58 is welded to a flange 136 on the operator output shaft 28, and a jaw clutch or coupling between shaft 28 and pilot valve 88 is constituted by lugs 138 on the former and lugs 140 on the latter. (This coupling will be described in greater particularity hereafter with reference to FIGURES 6A to 6E.)

A U-shaped chamber 142 is cast into the housing in the general area of wall 56. An opening 144 located just above the abutment 110 (FIGURE 3) passes through wall 56 and communicates with chamber 142. Similarly, an opening 146 located just below abutment 112 passes through wall 56 and communicates with chamber 142. The space 148 is in effect a sump which, as described hereafter, is connected to an internal drain of the hydraulic system. A hole 150 (FIGURE 2) provides communication between sump 148 and the gap between bushing 62 and a roller bearing assembly 152 rotatably mounting pilot valve 88. Through a bore 154, having a valve seat 156 therein, communication thereby may be established between chamber 142 and sump 148, A piston or plunger 158 is reciprocable within a cylindrical bore 159 cast in the housing, and is connected to a valve stem 160 by pin 162. Stern 160 is reciprocable in a bearing 164 mounted in a ring 166 that is retained in place by a cap screw 168. A compression coil spring 170 bottomed against ring 166 urges plunger 158 upwardly. It will be noted that the lower end of stem 160 is adapted to mate with the valve seat 156 to thereby prevent the interchange of a liquid between chamber 142 and sump 148.

The open right upper portion of housing 48 (FIGURE 2) is closed by a head secured by bolts 182. A line connection is indicated at 184, the head 180 having an annular flange 186 for connection as a flanged line coupling. A channel 188 in head 180 provides communication between line connection 184 and a further cylindrical bore 190 in the housing.

The open right end of housing 48 (FIGURE 2) is closed by a plate 192 mounting a further roller bearing assembly 194 for supporting pilot valve 88. A worm gear 196 is keyed on the end shaft portion of pilot valve 88, and a meshing worm 198 is rotatably supported in roller bearing assemblies 200 and 202 (FIGURE 4). The bearing assemblies are retained by cover plates 204 and oil seals 206. The end shaft portion 210 of the worm 198 has splines 208 for accommodating a manually operable crank, handwheel or the like.

A piston or plunger 212 is reciprocable in the cylindrical bore 190 and is connected to a rod 214 by a pin 216. Rod 214 is reciprocable in bearings 218 and 220 mounted in a ring 222 which is retained in place by a cap screw 224. The plunger 212 is urged upwardly by a compression coil spring 226 bottomed against ring 222. An arcuate segment 228 secured to the worm gear 196 by cap screws 230 has ends 231 which comprise abutments directly engageable by the rod 214 in the position shown upon a predetermined rotation of the gear. However, it will be evident that if rod 214 moves to the limit of its upward movement, rotation of worm gear 196 will be unlimited.

A fitting 232 adapted to be flange coupled to a hydraulic line is tapped into the housing 48 and communicates with the channel 96. ports 94 and 92, groove 90 and flats 98 and 99. A further fitting 234 is tapped into the housing 48 in communication with sump 148 and is adapted to be flange coupled to a hydraulic line.

Referring now back to FIGURE 1, the hydraulic system which operates the servomechanism or operator 2 will now be described, it being understood that the hydraulic circuit elements per se are conventional and are described merely as an example of one application of the invention. Oil enters the system through line 236, which is connected to the high pressure lubricating oil system of the steam turbine. After a hand valve 238 the line 236 branches off into a line 240. After two flow restricting orifices 242 and 244, line 240 branches off into a first line 246 leading to the line connection 184 (previously described with reference to FIGURE 2), and a second line 248 leading to a valve 250. A second branch 252 of line 236 leads to valve 250, and when a spool 254 of this valve is in its extreme left-hand position (FIGURE 1) the flow of oil is permitted from branch 252 to a line 256 which is connected to the previously mentioned fitting 232. A piston 258 operatively connected to spool 254 normally is urged to the left against the force of a spring 260 by oil pressure in the line 248, but when, due to a drop in said pressure, spool 254 is caused to move to its right-hand position (FIGURE 1) communication is established between line 256 and a drain connection 262 via a clearance 264. It will be evident that the pressure of oil in line 246 normally will act on pistons 158 and 212 (FIGURE 2) to force them downwardly against the opposition of springs 170 and 226, respectively. However, upon a failure of such pressure in line 246 piston 158 will be allowed to move upwardly under the action of spring 170, lifting valve stem 160 from seat 156. Likewise, plunger 212 will be allowed to move upwardly against the action of spring 226, lifting rod 214 out of the path of the arcuate abutment 228.

An overspeed tripping device is indicated generally at 266. Devices of this type are conventional, a detailed description therefore being unnecessary, and one may comprise valve means for opening the line 240 to internal drain 268 when the speed of a turbine or the like exceeds a predetermined safe maximum speed. Device 266 is of the type which must be manually reset after it has been tripped to dump the line 240 to drain 268.

A positive displacement pump 270 is driven directly from the shaft of the steam turbine, and draws oil from a line 272 connected to the lubricating oil system. Pump 270 discharges against an adjustable locked orifice 274, the discharge pressure in line 276 having an approximate squared relationship with respect to the turbine speed, and against a manual test valve 278. A pressure release valve 280 and a pressure gauge 282 also are provided. The discharge of pump 270 is recirculated back to the pump inlet through a line 284. A conventional valve 286 is responsive to pressure in a line 288, which is connected to the outlet of pump- 270. Upon the attainment of a predetermined pressure in line 288, indicating an excessive speed of the turbine, valve 286 operates to connect a branch 290 of line 240 to a drain line 292. It will be evident that upon the operation of valve 286 to open line 290 to drain 292, a drop in oil pressure will occur in line 240 and the branches thereof 246 and 248.

The operation of the aforedescribed mechanism will now be described, and in connection therewith supplemental reference will be made to FIGURES 6A to 6B, inclusive. These figures, which are intended to be schematic, represent the various relationships between the pilot valve and the vanes during different stages of operation and as viewed in FIGURE 3. Reference hereafter to clockwise and counterclockwise rotation of the pilot valve, vanes and other elements should be understood as when viewed according to FIGURE 3 and FIGURES 6A to 6E. When the steam valves 4 are closed, vanes 66 and 68 are in the position shown in FIGURES 6A and 6D; in other words, they are at the limit of counterclockwise rotation as viewed in FIGURE 3. Rotation of vanes 66 and 68 in a clockwise direction, i.e. toward their respective positions shown in FIGURE 63, tends to open valves 4, it being understood that such clockwise rotation of the vanes and of the sleeve 58 is resisted by springs 44 and 46 acting through shaft 24. When vanes 66 and 68 are rotated to the limit of their clockwise rotation, as shown in FIGURES 6C and 6E, the valves 4 are completely open. As mentioned, such clockwise rotation of the vanes and of shaft 24 can be effected only by overcoming the resisting action of torsion springs 44 and 46. It will be noted that the jaw coupling or clutch comprising the lugs 138 rigid with sleeve 58 and the lugs 148 on pilot valve 88 also is illustrated in FIGURES 6A to 6B.

Assume now that the steam valves 4 are closed, the vanes and pilot valve being in their respective positions indicated by FIGURE 6A, and that before it is desired to open these valves the oil system of the turbine is operating properly and high pressure oil is standing in line 236 (FIGURE 1). With valve 238 open, oil under pres sure flows through lines 240 and 246 to the plungers 158 and 216 (FIGURE 2); oil also flows through line 248 to valve 250, efi'ecting the movement of spool 254 to the left and permitting the flow of oil through lines 252 and 256 to the connection 232. The valve 286 constitutes a primary overspeed control and device 266 constitutes a secondary overspeed control, but since the turbine shaft is not rotating when the valves 4 are closed, neither of the drains 268 and 292 will be open. By virtue of the high pressure oil acting thereon, plungers =158 and 216 will be in their lowermost positions as shown in FIGURE 2.

Referring to FIGURES 6A, 6B and 6C (FIGURE 6B corresponds to FIGURE 3) when the lugs 140 are in the positions shown therein with respect to lugs 138, the channels 105, are in the positions shown in FIGURE 3 with respect to the ports 82, 86.

For any setting of the steam valves 4, during normal hydraulic operation of the servomechanism, the positions of lugs 140 with respect to lugs 138 are as shown in FIG- URES 6A, 6B and 6C, i.e. the lugs 140 are positioned slightly clockwise from or ahead of lugs 138. Now, if pilot valve 88 is rotated clockwise by a manual cranking of worm 198, flat 99 will uncover port 82, permitting oil under pressure to flow from the channel 96, ports 92 and 94 and groove 90 past the flat 99 and into a chamber designated A. Similarly, fiat 98 will uncover port 86, permitting high pressure oil to flow past flat 98 and through port 86 into a chamber designated B. The liquid pressure in chambers A and B, acting against vanes 66 and 68 in a clockwise direction, causes the vanes to follow the pilot valve 88 in a clockwise direction. The sleeve 58 and shaft 24 are driven in a clockwise direction by such movement of the vanes, which movement is opposed by the torsion springs 44 and 46. Such clockwise notation of shaft 24, of course, results in opening of the valves 4 by the cam assemblies and 22. The driving of vanes 66 and 68 continues until they have caught up wit the pilot valve 88, that is, until the ports 82 and 86 no longer are uncovered by the flats 99 and 98, respectively. As an example, assume that pilot valve 88 was rotated to a position shown in FIGURE 3. The vanes 66 and 68 would be driven clockwise until they reach the condition shown in FIGURE 3 and FIGURE 6B, and in which the ports 82 and 86 are covered by the pilot valve 88.

Two other chambers, C" and D, are identified in FIGURE 3, and these chambers are connected, via passages 120, 124 and 126, 130 to the passage 108 and 6 sump 148, the sump being connected to an internal drain in the hydraulic system by connection 234. Thus, in the course of clockwise rotation of vanes 66 and 68 oil may be displaced from chambers C and D to the drain.

It should be noted that the opening of the steam valves is in no way dependent upon the driving of lugs 138 by lugs 140, but rather that the lugs 140 stay ahead of (clockwise of) the lugs 138. The driving of sleeve 58 and shaft 24 to open the steam valves during normal hydraulic operation is effected solely by oil pressure in chambers A and B acting on vanes 66 and 68 which act in much the same manner as pistons. It will be evident that the extent of rotation of vanes 66 and 68 and sleeve 58 is directly proportionate to the amount of rotation of pilot valve 88 initially efiected by a manual cranking of worm 198. Thus, if by manual cranking of worm 198 the pilot valve 88 is rotated clockwise to an extent where its lugs 140 are positioned as shown in FIGURE 6C, vanes 66 and 68 and sleeve 58 will be driven to their extreme clockwise position wherein the ports and 86 again will be closed and the steam valves 4 will be opened.

In a balanced, stable condition of the servomechanism as, for example, in FIGURE 3, the torsion springs 44 and 46 continuously exert a counterclockwise force on sleeve 58, but this force is equally opposed by oil pressure in chambers A and B. Ordinarily, due to the leakage of oil from chambers A and B springs 44 and 46 would be able gradually to move vanes 66 and 68 in a counterclockwise direction. However, such counterclockwise movement would move ports 80 and 86 relative to the flats 98 and 99 of the pilot valve 88, and these ports would be uncovered to admit more high pressure oil to chambers A and B to maintain the stabilized condition. Consequently, in a stabilized condition the ports 82 and 86 may not be completely covered, but are open by perhaps a very small amount to permit a small flow of oil to chambers A and B. Compensation is thus made for the aforementioned leakage of oil.

With the steam valve 4 now fully opened and the servomechanism in the condition shown in FIGURE 6C, the steam valve may be closed in one of three ways: (a) by manual operation of worm 198, (b) by operation of either the primary or secondary overspeed tripping means, or (c) upon failure of the turbine oil system.

The steam valves may be closed by rotation of worm 198 in a direction to move pilot valve 88 counterclockwise (FIGURE 3). Such counterclockwise rotation causes channels and 107 to uncover ports 82 and 86, respectively. Since channels 105 and 107 communicate with the sump 148 via groove 106, ports 102 and 104, and passage 108, chambers A and B will be connected to the drain. The drop in oil pressure in chambers A and B will permit springs 44 and 46 to rotate shaft 24, sleeve 58 and vanes 66 and 68 in a counterclockwise direction, thereby also efie'cting the closing of steam valves 4. Again, the steam valves will be closed only to an extent proportionate to the amount of rotation of pilot valve 88, and if the pilot valve is rotated counterclockwise from the FIGURE 6C to the FIGURE 6B or FIGURE 3 position the vanes 66 and 68 will follow counterclockwise until the ports 82 and 86 are again covered. If the vanes 66 and 68 continue counterclockwise past the position wherein the ports 82 and 86 are closed, these ports will be uncovered by the flats 98 and 99 to admit high pressure oil to chambers A and B, with the consequences previously described. Complete closing of the steam valve 4, of course, is effected by movement of pilot valve 88 to the limit of its counterclockwise rotation.

At this point it should be noted that under normal operating conditions, when high pressure oil is acting downwardly on plunger 212, rod 214 is disposed in the path of abutment 228 and thereby limits the rotation of worm gear 196 and pilot valve 88. Thus, when worm gear 196 is rotated counterclockwise to bring the abutment 228 into engagement with rod 214 the pilot valve 88 will effect the full opening of steam valves 4, and clockwise rotation of worm gear 196 to bring the other end of abutment 228 into engagement with rod 214 will effect full closing of the steam valves. During normal hydraulic operation, by virtue of the rotation-limiting rod 214 the limit of counterclockwise rotation of lugs 140 is shown in FIGURE 6A and the limit of clockwise rotation is shown in FIGURE 6C. Springs 44 and 46 effect the urging of shaft 24- and lugs 138 in a counterclockwise direction (FIGURES 6A, 6B and FIGURE 60) to close the steam valves, but lugs 140 are positioned ahead of, rather than behind, lugs 138 in a clockwise direction. It will be evident, therefore, that ordinarily manual rotation of pilot valve 88 cannot be effective to drive shaft 24 through lugs 138 and 140 to open the steam valves in opposition to springs 44 and 46. In other words, lowered rod 214 prevents the rotation of lugs 140 to the positions thereof shown in FIGURE 6D, where lugs 140 are behind lugs 138 and further rotation would drive sleeve 58 to open the steam valve. This latter aspect, however, will be discussed more fully hereafter.

Closing of the steam valves also may be effected automatically upon the attainment of an excessive turbine speed. The valve tripping means for closing the steam valve when the speed of the turbine reaches, say, 110% of the design full power speed. The device 266 constitutes a secondary overspeed tripping device for closing the steam valves when the speed of the turbine reaches, say, 115% of the design full power speed. Both the primary and secondary overspeed tripping means effect the draining of line 246, either through drain 292 or drain 268. As previously described, under normal hydraulic operation oil pressure in line 246 acts downwardly on plunger 158 to position the stem 160 against valve seat 156. Upon a failure of such pressure, however, spring 170 is permitted to lift valve stem 160 from seat 156. Assuming now that the steam valves 4 are open, with high pressure oil existing in chambers A and B, if the pressure in line 246 drops the stem 160 will be lifted to drain chambers A and B via openings 144 and 146, chamber 142, valve seat 156, hole 150, and sump 148. With the drainage of chambers A and B, high pressure oil no longer acts on vanes 66 and 68 in opposition to springs 44 and 46 which will, therefore, effect closing of the steam valves.

In the case of the primary overspeed control, when pump 270 is driven by the turbine at a predetermined high speed the back pressure exerted on the pump by orifices 274 will act through line 288 to open the valves 286, thereby connecting line 290 to drain 292. In the case of the secondary overspeed control device 266, when the turbine speed reaches, say, 115% of rated maximum speed, the line 246 will be connected to drain 268. In either case the effect is to lower the pressure in line 246 and cause the draining of chambers A and B through chamber 142. When the secondary overspeed tripping device 266 has been actuated, it must be manually reset to close the drain 268. However, when only the valve 286 has been opened, upon a resumption of normal turbine speed the drain 292 will be closed automatically. In the latter case, remembering that in the meantime the pilot valve 88 has not been changed from its original setting, the resumption of pressure in chambers A and B will effect a reopening of the steam valve 4 in a manner previously described.

Closing of the steam valves 4 automatically takes place if the turbine oil system fails or is operating unsatisfactorily. 1f the oil pressure in line 236 drops the pressure will drop also in the line 256 leading to connection 232. Line 256, it will be recalled, feeds chambers A and B via the groove 90 and flats 98, 99, etc. The oil pressure in lines 240, 246 and 248 also will drop. Therefore, first, spring 260 is permitted to move spool 254 to the right (FIGURE 1), connecting line 256 to drain 262 286 constitutes the primary overspeed and, second, plungers 158 and valve stem 160 move upwardly to connect chambers A and B to drain line 234 via chamber 142 and sump 148. By the draining of chambers A and B torsion springs 44 and 46 are permitted to close steam valves 4.

In certain cases, even through the pressure in the turbine oil system is not sufficient to operate the servomechanism or operator 2, it may be desired nevertheless to open the steam valves 4. At such time, in the absence of substantial oil pressure in line 246, rod 214 will be raised out of the path of abutment 228 and will not limit the manual rotation of pilot valve 88. By the clockwise rotation of pilot valve 88 (by manual cranking of worm 198) lugs will be brought to their positions indicated in FIGURE 6D. Upon further rotation of pilot valve 88 lugs 144 will drive lugs 138 in the manner of a jaw clutch, sleeve 58 and shaft 24 thereby being driven in the direction to open steam valves 4. This latter condition of the elements is illustuated in FIGURE 6E. Manual closing of the steam valves by springs 44 and 46 is permitted by the manual rotation of pilot valve 88 in a counterclockwise direction, i.e. from the FIGURE 6E to the FIGURE 6D position.

It will be understood that various departures from the above described embodiment of the invention may be made without departing from the scope thereof as defined by the following claims.

What is claimed is:

l. A servomechanism comprising a cylinder, a displaceable member within said cylinder, a source of hydraulic pressure for driving said member, an output member connected to said displaceable member for transmitting movement thereof, a pilot valve member having means for the hydraulic control of the operation of said displaoeable member by said hydraulic pressure, said displaoeable member constituting a follower driven in direct relation to the movement of said valve member, intermeshing lugs on said output member and valve member, the lugs on said output member normally being disengaged from and following the lugs on said valve member, means for operating said valve member, means normally preventing movement of said valve member to an extent that the lugs on the valve member engage and drive the lugs on the output member, and means operable to render inoperative the last-mentioned means, whereby the said output member may be driven directly by said valve member.

2. A servomechanism comprising a cylinder, a displaceable member within said cylinder, a source of hydraulic pressure for driving said member, an output member connected to said displaceab'le member for transmitting movement thereof, a pilot valve member having means for the hydraulic control of the operation of said displaceable member by said hydraulic pressure, said displaceable member constituting a follower driven in direct relation to the movement of said valve member, intermeshing lugs on said output member and valve member, the lugs on said output member normally being disengaged from and following the lugs on said valve member, means for operating said valve member, means responsive to and operable by said hydraulic pressure to prevent movement of said valve member to an extent that the lugs on the valve member engage and drive the lugs on the output member, the last-mentioned means being rendered inoperable upon a failure of said hydraulic pressure, whereby the said output member may be driven directly by said valve member.

3. A servomechanism comprising a cylinder having a displaeeable member there-in and defining therewith a chamber, a source of hydraulic pressure for driving said displaceable member, means providing a drain, a valve having a pair of elements, said elements being relatively movable in one direction to an open position wherein said chamber is connected to said source and in the opposite direction to an open position wherein said charnher is connected to said drain, the elements having a closed position intermediate the aforementioned open positions, said displaeeable member constituting and providing the mechanical output of the servomechani-sm and being connected to one of said elements to operate the same, and the other of said elements constituting mechanical input means for controlling the operation of the servomechanism, and means automatically responsive to to a predetermined drop in pressure at said hydraulic source to drain said chamber regardless of the position of said elements.

4. A servomechamism comprising a cylinder having a displaceable member therein and defining therewith a chamber, a source of hydraulic pressure for driving said displaceable member, means providing a drain, a valve having a pair of elements, said elements being relatively movable in one direction to an open position wherein said chamber is connected to said source and in the opposite direction to an open position wherein said chamber is connected to said drain, the elements having a closed position intermediate the aforementioned open positions,

said displaceable member constituting and providing the mechanical output of the servomechanism and being connected to one of said elements to operate the same, and the other of said elements constituting mechanical input means for controlling the operation of the servomechanism, a clutch adapted to connect said other element to said displaceable member to drive the same, and means normally preventing engagement of said clutch but responsive to a predetermined drop in pressure at said source to permit such engagement, whereby said displaceable member is normally drive by hydraulic pressure but may be directly driven by operation of said other element upon a drop in said pressure.

5. A servomechanism comprising a cylinder, a vane within said cylinder, means defining with said vane and cylinder a chamber, a sleeve mounting said vane for displacement in a first direction by hydraulic pressure in the chamber, means resiliently urging said vane in a second and opposite direction in opposition to said pressure, motion transmitting means transmitting movement of said vane to perform mechanical Work, a port in said sleeve for the ingress and egress of liquid in said chamber, a pilot valve member Within said sleeve and movable relative thereto, a source of hydraulic pressure, means providing a drain, said member normally occupying a position with respect to said sleeve to close said port, and said member being movable from said position in said first direction to open said port to said source and movable in said opposite direction to open said port to said drain, whereby said member constitutes the input means of the servomechanism, with movement of the member resulting in proportionate displacement of said vane.

6. Servomechanism according to claim 5, including means for transmitting motion of said pilot valve membet to drive the first-mentioned motion transmitting means, and means responsive to the pressure at said source preventing operation of the second-mentioned motion transmitting means when said pressure exceeds a predetermined minimum.

7. Servornechanism according to claim 5, including a normally disengaged clutch connecting said pilot valve member and said motion transmitting means, and means responsive to a predetermined drop in the pressure at said source to engage said clutch to permit direct driving of said motion transmitting means by said pilot valve memher.

8. Servomechanism according to claim 5, including means automatically responsive to a predetermined drop in the pressure at said source for draining said chamber regardless of the position of said pilot valve member relative to said port.

References Cited in the file of this patent UNITED STATES PATENTS 1,876,104 Tucker Sept. 6, 1932 1,947,991 Jessup Feb. 20, 1934 2,091,669 Bryant Aug. 31, 1937 2,261,462 Gabolis Nov. 4, 1941 2,383,773 Chisholm Aug. 28, 1945 2,654,347 Clark Oct. 6, 1953 2,915,044 Nelson Dec. 1, 1959 2,939,428 Ostwald June 7, 1960 

1. A SERVOMECHANISM COMPRISING A CYLINDER, A DISPLACEABLE MEMBER WITHIN SAID CYLINDER, A SOURCE OF HYDRAULIC PRESSURE FOR DRIVING SAID MEMBER, AN OUTPUT MEMBER CONNECTED TO SAID DISPLACEABLE MEMBER FOR TRANSMITTING MOVEMENT THEREOF, A PILOT VALVE MEMBER HAVING MEANS FOR THE HYDRAULIC CONTROL OF THE OPERATION OF SAID DISPLACEABLE MEMBER BY SAID HYDRAULIC PRESSURE, SAID DISPLACEABLE MEMBER CONSTITUTING A FOLLOWER DRIVEN IN DIRECT RELATION TO THE MOVEMENT OF SAID VALVE MEMBER, INTERMESHING LUGS ON SAID OUTPUT MEMBER AND VALVE MEMBER, THE LUGS ON SAID OUTPUT MEMBER NORMALLY BEING DISENGAGED FROM AND FOLLOWING THE LUGS ON SAID VALVE MEMBER, MEANS FOR OPERATING SAID VALVE MEMBER, MEANS NORMALLY PREVENTING MOVEMENT OF SAID VALVE MEMBER TO AN EXTENT THAT THE LUGS ON THE VALVE MEMBER ENGAGE AND DRIVE THE LUGS ON THE OUTPUT MEMBER, AND MEANS OPERABLE TO RENDER INOPERATIVE THE LAST-MENTIONED MEANS, WHEREBY THE SAID OUTPUT MEMBER MAY BE DRIVEN DIRECTLY BY SAID VALVE MEMBER. 